The present invention relates to, in general, to a hydraulic binder, and more particularly to a hydraulic binder having as main component cement and iron-(II)-sulfate added to the cement for reduction of chromate.
Cement is typically used in the construction industry as finely ground hydraulic binder for making concrete, mortar, concrete stones and finished parts. Oftentimes, cement is manually processed. This is disadvantageous because typical cement contains chromate which can trigger allergic reactions such as skin eczema, so-called cement dermatitis or bricklayer scabies.
Chromate-containing cement includes up to 100 ppm of chromium(VI) compounds (chromates) of which about 20% are soluble. Soluble chromate is the cause of the allergic cement eczemas. By utilizing cement which is almost free of chromate and cement-containing preparations that are low in chromate, for example, tile adhesive or dry mortar, diseases of this type can be effectively eliminated. For that reason, cement-containing materials which are handled manually are produced exclusively with low content of chromate. Chromate-containing cement means a cement which contains less than 2 ppm of water-soluble chromium(VI) relative to the dry mass.
It is known, to decrease the chromate content in cement through addition of a reducing agent, e.g. iron-(II)-sulfate. German patent publication no. DE 197 44 035 A1 describes the addition of dry iron-(II)-sulfate particles to cement at an amount of 0.01 to 1 wt. %, when the cement is withdrawn from a large silo. During preparation of the mortar or concrete mixture, the granular iron-(II)-sulfate dissolves in the mixing water and contacts the chromate(VI) during mixture to thereby chemically reduce it.
Also Manns, W.; Laskowski, Ch. describe in an article, entitled Eisen-(II)-sulfat als Zusatz zur Chromatreduzierung [Iron-(II)-sulfate for chromate reduction] in BE-Z: Beton [Concrete], journal 2/1999, pages 78–85, the use of dry powdery iron-(II)-sulfate for chromate reduction.
Dry iron-(II)-sulfate looses, however, effectiveness as a result of oxidation with atmospheric oxygen. Therefore, iron-(II) sulfate has been added to cement only at a time when the cement is withdrawn from the large silo to thereby decrease the risk of undesired reaction as the granular iron-(II) sulfate is added to the cement.
German patent publication no. DE 100 14 468 A1 describes the production of a building material made from a mixture of cement, water and additives and the addition of moist iron-(II)-sulfate, so-called green (iron) vitriol, to the mixture. To improve handling of moist green vitriol, a dry material is added, e.g., ground limestone.
It would be desirable and advantageous to provide an improved hydraulic binder which is more cost-efficient and yet reliable in use.